Structural Model and Computer Modeling Study of Allophane

Abstract

A model of an allophane nanoball is proposed. The model structure is characterized by a Si/Al ratio of 0.49, has external and internal diameters of 50 and 40 Å, respectively, and contains six holes of about 7 Å size connecting the internal void of the nanoball with external space. The calculated XRD pattern and Raman spectrum of the structure are in a good agreement with the corresponding experimental data. Molecular dynamics calculations of hydrated allophane have shown that the model reproduces the main experimental findings such as the adsorption of water molecules in the void of allophane or the exchange between the “internal” and “external” water. The adsorption of water molecules occurs mostly in the regions with negative electrostatic potential, where the molecules find an environment close to that in bulk liquid water that explains the high water retention by this aluminosilicate. The allophane model can be used as a basis in further refinements of its structure as well as in molecular modeling studies of this aluminosilicate.

Structure and distribution of allophanes, imogolite and proto-imogolite in volcanic soils

“…Regarding the recent boom in the nanotechnology field, the term "nano-ball allophanes" was recently used (Abidin et al, 2007;Ghoneim et al, 2001;Khan et al, 2006). Structural models have been proposed which consist of hollow nanospheres composed of six pores (Abidin et al, 2006;Creton et al, 2008).…”

Nanoclays from an Andisol: Extraction, properties and carbon stabilization

“…Irrespective of chemical composition and origin, the unit particle of allophane is a hollow spherule ( Fig. 1) with an outer diameter of 3.5-5.0 nm (Abidin et al, 2007;Creton et al, 2008). The 0.7-1.0 nm thick spherule wall is composed of an outer Al octahedral (gibbsitic) sheet and an inner Si sheet.…”

Characterization of Allophane from Gamalama Volcanic Soil, North Maluku, Indonesia

“…X-ray diffraction of Gamalama volcanic ash-soil ( Allophane particles are irregular spherule and tend to form porous nano size aggregates with a dimeter 3.5-5.0 nm [14][15][16]. Characterization using TEM (Fig.…”